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<html>
<head>
<title>
HEX_GRID_DATASET - Interactive Creation of Hexagonal Grid Datasets
</title>
</head>
<body bgcolor="#EEEEEE" link="#CC0000" alink="#FF3300" vlink="#000055">
<h1 align = "center">
HEX_GRID_DATASET <br> Interactive Creation of Hexagonal Grid Datasets
</h1>
<hr>
<p>
<b>HEX_GRID_DATASET</b>
is a FORTRAN90 program which
allows the user to interactively
create a dataset of points on a hexagonal grid.
</p>
<p>
The user specifies just a few quantities:
<ul>
<li>
<b>(X1,Y1)</b>, the lower left coordinate of a box.
</li>
<li>
<b>(X2,Y2)</b>, the upper right coordinate of a box.
</li>
<li>
<b>NODES_PER_LAYER</b>, the number of nodes to use on the
first line, from <b>(X1,Y1)</b> to <b>(X2,Y1)</b>.
</li>
</ul>
</p>
<p>
This is all it takes to define the grid. Note that the points
<b>(X1,Y1)</b> and <b>(X2,Y1)</b> will be grid points, but generally
the grid will not quite reach <b>(X1,Y2)</b> and <b>(X2,Y2)</b>.
</p>
<p>
Once the dataset is defined and computed, it is written to a file.
The user may then construct another dataset, or terminate the program.
</p>
<p>
Here is some more information on the construction of the grid:
</p>
<p>
The hexagonal grid is defined on a coordinate box whose lower left
corner is (X1,Y1) and whose upper right corner is (X2,Y2).
</p>
<p>
All nodes of the grid lie on one of <b>LAYERS</b> horizontal lines.
The first of these lines is the line from (X1,Y1) to (X2,Y1).
Each successive line is a distance <b>HY</b> units higher.
</p>
<p>
On all the odd numbered lines, there are <b>NODES_PER_LAYER</b> points,
equally spaced from X1 to X2, with a spacing of <b>HX</b>.
</p>
<p>
On the even numbered lines, there are <b>NODES_PER_LAYER</b>-1 points,
whose values are the midpoints of successive intervals on
an odd numbered line. (The grid is staggered).
</p>
<p>
In order to maintain the hexagonal structure, the following relationship
is required between <b>HX</b> and <b>HY</b>:
<pre>
<b>HY</b> = <b>HX</b> * sqrt ( 3 ) / 2.
</pre>
</p>
<p>
Here is an image of a hexagonal grid with <b>NODES_PER_ROW</b> = 21
and <b>LAYERS</b> = 24, and a total of <b>N</b> = 492 nodes.
<img src = "../../datasets/hex_grid/hex_grid_01_21_24_492.png"
height = "400"
width = "400">
</p>
<h3 align = "center">
Licensing:
</h3>
<p>
The computer code and data files described and made available on this web page
are distributed under
<a href = "../../txt/gnu_lgpl.txt">the GNU LGPL license.</a>
</p>
<h3 align = "center">
Languages:
</h3>
<p>
<b>HEX_GRID_DATASET</b> is available in
<a href = "../../cpp_src/hex_grid_dataset/hex_grid_dataset.html">a C++ version</a> and
<a href = "../../f_src/hex_grid_dataset/hex_grid_dataset.html">a FORTRAN90 version</a> and
<a href = "../../m_src/hex_grid_dataset/hex_grid_dataset.html">a MATLAB version</a>.
</p>
<h3 align = "center">
Related Data and Programs:
</h3>
<p>
<a href = "../../f_src/faure_dataset/faure_dataset.html">
FAURE_DATASET</a>,
a FORTRAN90 program which
creates a Faure quasirandom dataset;
</p>
<p>
<a href = "../../f_src/grid_dataset/grid_dataset.html">
GRID_DATASET</a>,
a FORTRAN90 program which
creates a grid sequence and writes it to a file.
</p>
<p>
<a href = "../../f_src/hex_grid/hex_grid.html">
HEX_GRID</a>,
a FORTRAN90 library which
computes elements of a hexagonal grid dataset.
</p>
<p>
<a href = "../../f_src/hex_grid_angle/hex_grid_angle.html">
HEX_GRID_ANGLE</a>,
a FORTRAN90 library which
computes elements of an angled hexagonal grid dataset.
</p>
<p>
<a href = "../../f_src/latin_center_dataset/latin_center_dataset.html">
LATIN_CENTER_DATASET</a>,
a FORTRAN90 program which
creates a Latin Center Hypercube dataset;
</p>
<p>
<a href = "../../f_src/latin_edge_dataset/latin_edge_dataset.html">
LATIN_EDGE_DATASET</a>,
a FORTRAN90 program which
creates a Latin Edge Hypercube dataset;
</p>
<p>
<a href = "../../f_src/latin_random_dataset/latin_random_dataset.html">
LATIN_RANDOM_DATASET</a>,
a FORTRAN90 program which
creates a Latin Random Hypercube dataset;
</p>
<p>
<a href = "../../f_src/niederreiter2_dataset/niederreiter2_dataset.html">
NIEDERREITER2_DATASET</a>,
a FORTRAN90 program which
creates a Niederreiter quasirandom dataset with base 2;
</p>
<p>
<a href = "../../f_src/normal_dataset/normal_dataset.html">
NORMAL_DATASET</a>,
a FORTRAN90 program which
generates a dataset of multivariate normal pseudorandom values and writes them to a file.
</p>
<p>
<a href = "../../f_src/sobol_dataset/sobol_dataset.html">
SOBOL_DATASET</a>,
a FORTRAN90 program which
computes a Sobol quasirandom sequence and writes it to a file.
</p>
<p>
<a href = "../../f_src/uniform_dataset/uniform_dataset.html">
UNIFORM_DATASET</a>,
a FORTRAN90 program which
generates a dataset of multivariate uniform pseudorandom values and writes them to a file.
</p>
<p>
<a href = "../../f_src/van_der_corput_dataset/van_der_corput_dataset.html">
VAN_DER_CORPUT_DATASET</a>,
a FORTRAN90 program which
creates a van der Corput quasirandom sequence and writes it to a file.
</p>
<h3 align = "center">
Source Code:
</h3>
<p>
<ul>
<li>
<a href = "hex_grid_dataset.f90">hex_grid_dataset.f90</a>, the source code.
</li>
<li>
<a href = "hex_grid_dataset.sh">hex_grid_dataset.sh</a>,
commands to compile the source code.
</li>
</ul>
</p>
<h3 align = "center">
Examples and Tests:
</h3>
<p>
<ul>
<li>
<a href = "hex_grid_dataset_input.txt">hex_grid_dataset_input.txt</a>,
sample interactive input.
</li>
<li>
<a href = "hex_grid_dataset_output.txt">hex_grid_dataset_output.txt</a>,
output from the interactive run.
</li>
<li>
<a href = "../../datasets/hex_grid/hex_grid_10_18_171.txt">
hex_grid_10_18_171.txt</a>,
a sample hex grid dataset, with 10 nodes per layer, 18 layers,
and 171 points.
</li>
</ul>
</p>
<h3 align = "center">
List of Routines:
</h3>
<p>
<ul>
<li>
<b>MAIN</b> is the main program for HEX_GRID_DATASET.
</li>
</ul>
</p>
<p>
You can go up one level to <a href = "../f_src.html">
the FORTRAN90 source codes</a>.
</p>
<hr>
<i>
Last revised on 30 August 2005.
</i>
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